Nested constructs vs. sub-selects in SPARQL

The issue of subqueries in SPARQL has appeared in different papers as an extension point to the original SPARQL query language. Particularly, nested CONSTRUCT in FROM clauses are a feature that has been discussed as a potential input for SPARQL 1.1 which was resolved to be left out in favour of select subqueries under the - unproven - conjecture that such subqueries can express nested construct queries. In this paper, we show that it is indeed possible to unfold nested SPARQL construct queries into subqueries in SPARQL 1.1; our transformation, however, requires an exponential blowup in the nesting depth. This suggests that nested construct queries are indeed a useful syntactic feature in SPARQL that cannot compactly be replaced by subqueries